Ireland are sweating on the fitness of out-half Jonathan Sexton ahead of their crunch 'Cup final' clash with Argentina at Lansdowne Road on Saturday.

With Declan Kidney admitting his side probably need a win against the Pumas to secure their position in the world's top eight ahead of next month's World Cup draw, Ireland's coach will be hoping that his out-half is passed fit.

Ireland are already resigned to being without six of their best players and now Sexton is a doubt after injuring his groin while warming up at Thomond Park.

Four years on from the 17-3 success against Argentina in Dublin that secured Ireland's top-eight ranking in Kidney's first November series in charge, he is faced with a similar scenario next weekend.

Under the complicated ranking system, Ireland could drop from their current position of seventh should they slip up at home against Argentina and Scotland defeat Tonga by more than 15 points.

"It's the same situation as four years ago but with just a completely different age profile of a squad," said Kidney, for whom Eoin Reddan also remains a doubt ahead of the crunch clash.

"Their enthusiasm has been infectious and I think you saw a taste of that. So it's the same mathematical scenario but a totally different squad scenario.

"And it's a completely different Argentina squad. They're in a better shape; they're more hardened. When we played them four years ago you'd catch them because they'd probably get three weeks together in a whole season.

"Now they're at the end of maybe 10 or 11 weeks together. They're a seriously impressive side now."

Were Ireland to slip out of the top eight of the rankings, the IRFU would be highly unlikely to renew Kidney's contract when it expires after the Six Nations so he needs a big performance from his side next Saturday.

Lock Donncha O'Callaghan has stressed the importance of the clash against Ireland's familiar foes.

"It is what our November will be judged on," he said. "It's Cup final stuff, that's how it feels already. We've had three great weeks but it doesn't matter for anything if we don't get a result."